This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The primary subject of this project is the Mtr4 protein, a highly conserved and essential eukaryotic protein that plays a central role in RNA surveillance and decay pathways. Mtr4 is an RNA helicase that acts in complex with Trf4 (an RNA polymerase) and Air2 (a zinc finger protein) to form the ?TRAMP? complex. By an unknown mechanism, this complex identifies RNAs for degradation, tags them with a short poly-A tail, and then delivers them to the exosome for exonucleolytic degradation. In order to elucidate the structural details of TRAMP-dependent RNA surveillance, we are determining crystal structures of Mtr4 and relevant complexes. Our current Mtr4 crystals diffract poorly on a home source, requiring synchrotron radiation for structure determination.